The invention relates to a method for starting a short message transmission in a mobile telephone network comprising at least one short message service centre having an identity and transmitting short messages; at least one gateway mobile exchange forwarding short messages; at least one mobile exchange forwarding short messages; a subscriber capable of receiving short messages; and a home location register having a subscriber-specific list of identities of short message service centres that have transmitted rejected short messages, a subscriber-specific short message transmission starting message from the home location register activating the short message service centre to transmit a short message to the gateway mobile exchange in order for the short message to be forwarded to the subscriber, wherein the rejected short messages are stored in the short message service centre.
In cellular radio networks it is known to send short messages via a short message service centre separate from the cellular radio network. One system for sending and forwarding short messages is described in GSM 03.40, February 1992, Technical Realization of Short Message Services Point to Point, ETSI/PT. The specification describes the interfacing of a short message service centre (SC) to the mobile exchange of a cellular radio network, and the operation of the SC when it sends and forwards short messages from outside the cellular radio network and from one subscriber (A subscriber) to another (B subscriber) in the cellular radio network, or to an external message means capable of receiving and/or sending short messages. The transfer of short messages over a radio path between GSM terminal equipment, a mobile exchange and a short message service centre is described more closely in GSM 04.11, February 1992, MS-BSS Interface--Support of Short Message Service (p-p), ETSI/PT 12.
FIG. 4 of the attached drawings shows a situation preceding the arising of the problem associated with the prior art. A short message service centre SC1 sends 400 a short message to a gateway mobile exchange GMSC, which requests 401 for routing information from the home location register HLR of the subscriber by a SendRoutingInfoForSM message. The HLR sends 402 the required routing information (Routing-Info), i.e. the identity of the mobile exchange of the assumed location area of the subscriber to the gateway mobile exchange GMSC, which sends 403 the short message (ForwardShortMessage) received by it to the mobile exchange VMSC/VLR of the assumed location area of the subscriber. As the subscriber is not reachable 404, the visitor location register VLR sets the MWF flag of the subscriber, i.e. the VLR message waiting flag, illustrated in FIG. 2. There is one message waiting flag for each International Mobile Subscriber Number IMSI. If there are messages addressed to the subscriber the transmission of which has not been completed successfully, the Message Waiting Flag is in the position True T, and if there are no messages addressed to the subscriber, the flag is in the position False F. If the flag is in the position T, the VLR monitors whether the subscriber establishes a connection to the mobile network. If the subscriber establishes a connection to the mobile network, the HLR of the subscriber has to be informed of the connection establishment. Moreover, as the subscriber has not been reachable, the VMSC/VLR sends 405 a negative acknowledgement message (ForwardShortMessageNegativeAcknowledge), which indicates to the GMSC that the subscriber is not reachable. The GMSC thereby sends 406 an activation message (SetMessageWaitingData) to the HLR of the subscriber, which message activates the HLR to make up 407 a Message Waiting Data List, i.e. a MWD list, in compliance with GSM 03.40. For each B subscriber the MWD list stores, on the basis of the IMSI of each subscriber and the MSISDN numbers msisdn associated with the IMSI, the addresses Sc1, Sc2 of short message centres SC storing short messages waiting to be transmitted to the subscriber. This list is shown in FIG. 3. The HLR of the subscriber indicates that the MWD list has been made up 407 by sending 408 an acknowledgement message (SetMWDPositiveAcknowledge) to the GMSC, which sends 409 a negative acknowledgement message (ShortMessageNack) indicating an unsuccessful short message transmission to the short message service centre SC1, which made the short message transmission attempt to the subscriber. The SC1 thereby stores 410 in its memory the short message, which it attempted to transmit to the subscriber. Short messages are stored in the memory of the SC in such a manner as shown in FIG. 1B, that is, the short messages SM 1 and SM 2 correspond to the MSISDN number MSISDN to which the messages are to be sent.
FIG. 5 shows a situation in which the subscriber is not reachable, and the MWD list of the HLR of the subscriber contains the identities of SCs storing short messages waiting to be transmitted to the subscriber in their memories. Further, in the situation shown in FIG. 5, an MWF flag is set in the VLR of the subscriber location area, which flag indicates that the HLR of the subscriber has to be informed if the subscriber establishes a connection with the network. Accordingly, when another short message service centre SC2 sends 501 a new short message (ShortMessage) to the same subscriber to which there has already been a short message transmission attempt, the GMSC requests for routing information for the short message from the HLR of the subscriber by sending 502 a routing information request message (SendRoutingInfoForSM). As the MWD list of the HLR already contains the identity of at least one SC that has attempted a short message transmission to the subscriber, but the subscriber has not been reachable, the HLR sends 504 a negative acknowledgement (RoutingInfoNack) to the routing information request made by the GMSC. The GMSC forwards information about the unsuccessful transmission of the short message by sending 505 a negative acknowledgement (ShortMessageNack) to the short message service centre SC2, which further stores the rejected short message in its memory, as shown in FIG. 1B. The short messages are stored in the memory of the SC on the basis of the MSISDN number of the recipient of the short message so that the messages SM 1, SM 2 to each MSISDN number are stored in connection with this particular MSISDN number MSISDN.
FIG. 6 shows a situation in which the subscriber recovers operation in the network, undergoes location updating, or changes its location area. In such cases, a short message can be transmitted to the mobile telephone of the subscriber, and the visitor location register VMSC/VLR within the area of which the subscriber registers sends 601 information (NoteMSPresent or UpdateLocation) about the reappearance of the subscriber in the network to the HLR of the subscriber. The transmission of NoteMSPresent takes place as the MWF (Message Waiting Flag) is set in the concerned VLR, and so the VLR will indicate to the HLR that the subscriber is again reachable. The indication that the subscriber is again reachable is forwarded to the HLR of the subscriber even in cases where this would not be necessary, e.g. when the subscriber re-registers in the network within the service area of the same VLR the area of which it left. When the HLR of the subscriber receives information indicating that the subscriber is again reachable in the network, it starts to send 602, 604 Alert messages to the SCs included in the MWD list of the concerned subscriber so as to indicate them that the subscriber has become active within the area of the cellular radio network and that the transmission of the short message to the mobile telephone of the subscriber can again be attempted. The HLR sends 602, 604 these messages (Alert SC1, Alert SC2) via the gateway mobile exchange GMSC/IWMSC to the respective short message service centres SC1 and SC2, and provides the messages 603, 605 (Alert (msisdn)) with the msisdn numbers of the subscriber. A situation described above may occur, e.g. when the subscriber has switched off the mobile telephone overnight and switches it on in the morning, or correspondingly, if the subscriber uses the mobile telephone at work and switches it on at the beginning of the working day. Alert messages initiate the transmission of the subscriber's short messages from the SCs through the cellular radio system to the subscriber. Short messages are stored in the SC on the basis of the subscriber's Mobile Station International PSTN/ISDN Number.
The problem to be solved by the invention arises when short messages to be transmitted to the subscriber are stored in at least one of the short message service centres SC1, SC2, and the subscriber has not been reachable for some reason, and so the transmission of the waiting short messages to the subscriber has failed. When the subscriber is connected to the network, the VLR within the service area of which this particular subscriber registers attempts to send information indicating that the subscriber has recovered operation in the network to the HLR of the subscriber. Now, if the indication message (NoteMSPresent), which the visitor location register VMSC/VLR of the subscriber location area sends 601 to the HLR of the subscriber, is lost, the HLR of the subscriber will not be provided effectively with an indication that the subscriber is again reachable, and thus the HLR will not send the alert message, the reception of which would enable the short message service centre SC1, SC2 to send the short message via the GMSC/IWMSC to the subscriber.
In other words, when the subscriber is again reachable and the VLR sends to the HLR a message indicating that the subscriber is again reachable, i.e. the NoteMSPresent message, the transmission of which is an unacknowledged service, the VLR will not receive an acknowledgement of the successful transmission of the message from the HLR. The VLR of the subscriber location area thereby sets its own MessageWaitingFlag MWF to a value False after having sent the above-mentioned indication message. Thus, if the indication message should be lost on its way to the HLR, e.g. due to the overload of the transmission network or the recipient HLR or for some other reason, it may happen that the MWD list of the HLR contains addresses of short message service centres SC1, SC2 storing short messages waiting to be transmitted to subscribers which actually are reachable within the area of the cellular radio network. At the same time, however, the MWF flag is not set in the VLR, i.e. the flag is set to the value False, and so the subscriber supposes that none of the SCs stores short messages waiting to be transmitted to it. In this situation, a normal short message transmission to a subscriber that is reachable will fail as the HLR conceives that the subscriber is not reachable. It is to be noted that the problem does not occur with priority short messages since an attempt is always made to deliver them to the subscriber irrespective of whether the subscriber is reachable or not.
In the prior art case, the problem situation will not ease off until the subscriber changes its location area and moves to the service area of another VLR, and the HLR of the subscriber is informed of this. In this kind of situation, the new VLR performs location updating by sending a location updating message to the HLR of the subscriber. According to the GSM recommendations, the location updating is an acknowledged service and so the location updating message cannot be lost unnoticed. On the receipt of the location updating message, the HLR deletes the identities of the short message centres, that is, the SC addresses, from the MWD list.
The above-described problem situation is extremely difficult for a subscriber always roaming within the service area of the same VLR, since, if it happens once that an indication that the subscriber is again reachable is lost between the VLR and the HLR, the subscriber will never more receive any normal short messages addressed to it. A typical feature of the present-day cellular radio systems is that the service area of a single VLR covers a very large geographical area, and so it is highly probable that in the above-described error situation the subscriber will not notice for a long time that there are short messages waiting to be transmitted to the subscriber.